The present invention relates to knitting needles for use in circular knitting machines of the dial and cylinder type.
Such knitting machines have long been known and used for the production of knitted goods. Such machines are capable of the fastest and highest production of any machines known. Efforts have been made, nevertheless, to increase the speed at which the machines operate, which is their rotational speed, and these efforts have included improved construction of the needles used in such machines. Examples of improved needle constructions are found in U.S. Pat. No. 3,464,237 to Alfred O. Kohorn, characterized by a needle having an integral shank and needle portion with cutouts on the back of the shank to reduce the needle weight and the needle contact area. Also, in U.S. Pat. No. 3,712,082 to Alfred O. Kohorn, there was disclosed the combination with a circular dial and cylinder type knitting machine of a thin guage straight unbent needle pressed against one groove side by a spring carried by the needle so that the spring engaged the opposite groove side in all positions of the needle. While such needles have proven successful in use, there have nevertheless been experienced the occasion of needle breakage, as machines have been run at ever higher speeds.
Needle breakage is due to vibration of the hook portions of the needles, which vibrations may result in the hook of one needle striking the hook of another needle, or simply due to metal fatigue. In the latter case, although there may not be actual striking of one needle against another, the metal of which the needle is made is reduced in strength by the fatigue induced by vibrations, so that even when normal loads are placed on the needle during its operation, they are sufficient to cause the needle to break.
Needle breakage is undesirable because with a hook of a needle broken off, that needle fails to knit, and accordingly the product produced is defective. Consequently, the machine must be shut down in order to replace the needle, thereby resulting in down time of the machine and loss of productivity.
Consideration of the problem of needle vibration, and particularly vibration of the hook, indicates that vibration in the needle is generated by the engagement of a butt or butts with the parts of the machine which define and provide the cam with which the butt engages in order to move the needle to and from knitting position in its groove. Thus, the vibrations are generated at the butt, and while they travel into the needle from the portion of the needle underlying or immediately adjacent the butt, the vibrations travel towards the forward end of the needle. The vibrations which reach the hook of the needle cause it to vibrate, with the deletorious effects above noted.